Effects of carbon segregation and interface roughness on the mobility of solid-liquid interface in Fe-C alloy: A molecular dynamics study

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The kinetic coefficients (μ) for the fcc Fe-(0–0.5 wt%)C alloy solidification and melting were investigated using molecular dynamics simulations. The activation energy for the diffusion of C atoms (QC) at the solid-liquid interface was calculated using the Debye-Waller factor <u2> to reveal the effect of C atoms dragging on the interface mobility. The influence of C segregation and interface roughness on interface mobility was also investigated. Simulation results show that for melting, the C content has a minor effect on the μ, and the μ is mainly ranged 18.1–19.4 cm/s•K, while for solidification, the μ linearly decreases with the increasing C content, and the μ is ranged 9.6–17.9 cm/s•K. In addition, a ‘platform’ zone was observed under low undercooling, in which the interface velocity is close to zero and suggests weak interface mobility, resulting from the segregation and dragging of C atoms at the interface. The ‘platform’ zone size linearly increases with the increasing C content. The QC increases with the increasing C content, which is ranged 0.71–0.91 eV for the fcc Fe-(0.1–0.4 wt%)C alloy solidification, indicating the C atomic motion is weakened and the C atoms dragging is reinforced due to C content increasing. Interface roughness and C atoms distribution analyses show that for the fcc Fe-C alloy solidification, a smooth solid-liquid interface is unfavorable for interface mobility, and the smooth interface is usually accompanied by the non-uniform distribution of C atoms. Therefore, increasing the interface roughness may be helpful for improving interface mobility and segregation for alloy solidification.